Dynamic vibration absorber

Abstract: A dynamic vibration absorber comprises a movable weight portion (1), a movable portion magnet means (2) provided for the movable weight portion (1), the movable portion magnet means comprising a magnet train (2) including a plurality of cylindrical magnets disposed coaxially in such a manner that adjacent cylindrical magnets have different magnetic poles, a fixed portion (4,5) provided in opposed relation to the movable weight portion (1) and a fixed portion magnet train (6) provided on the fixed portion (4,5) and comprising a plurality of magnets having magnetic poles different, in a stationary state, from magnetic poles of the cylindrical magnets disposed. The movable weight portion (1) is disposed in a vessel (3). The magnetic means are substituted with coil spring elements (17) for supporting the movable weight portion (1) horizontally. A fluid is filled up in an inner hollow portion of the movable weight portion. A magnetic damper means (10 to 13) is further disposed, which has a plurality of conductor plates (10) mounted on an outer peripheral surface of the movable weight portion (1) and a plurality of yokes (11) secured to an inner surface of the peripheral side portions (3a) of the cylindrical vessel at portions corresponding to the conductor plates (10), each of the yokes (11) having a pair of yoke portions facing each other, and a pair of magnets (12) are provided on the facing surfaces of the paired yoke portions with gap (13) into which the corresponding conductor plates (10) are inserted with gap.

Description: BACKGROUND OF THE INVENTION The present invention relates to a dynamic vibration absorber capable of suppressing vibrations in horizontal two-dimensional directions of a target or object structure. Generally, a dynamic vibration absorber includes an additional weight portion which is subjected to a force of inertia by vibrations, a rigidity element for generating a reaction force to the inertia force applied to the additional weight portion and a damping element for absorbing vibration energy. A conventional dynamic vibration absorber is constructed such that vibrations in a specified direction of a target structure are suppressed by vibrating an additional weight portion. Hence, if there are a plurality of directions in which vibrations are to be controlled, the vibration controlling equipment must contain the same number of dynamic vibration absorbers as that of directions of vibrations. A dynamic vibration absorber according to the preamble of the appended main claim is known from GB-PS 744041 which discloses an absorbing or damping system in a machine tool part lyable to self-induced vibration during operation. In this known damping system a movable weight is supported by spiral springs so that the movable weight can vibrate in any radial direction, i.e. in any direction of a vertical plane. The use of spiral springs means limited flexibility with respect to the effective spring constant. Furthermore, the installation of the spiral spring needs some effort when installing the vibration absorber. In US-A-4,471,331 there is disclosed a magnetically supported work fixture including a support for supporting a printed circuit board which has to be worked on. The support can be easily rotated within a horizontal plane. This is achieved by constructing the support with a downwardly projecting truncated cone section with circumferential steps in which permanent toroidal magnets are embodid. A mount is constructed with a cavity complementary to the projecting cone section and is provided with circular steps in which are embodid permanent toroidal magnets. When the projecting section of the support is placed in the mount cavity, the magnets in the support and in the mount are laterally alined while certain of the magnets in the support also are positioned to overlay the magnets in the mount. The polarity of the magnets is selected so that the overlaying magnets act to repel each other and hold the support sidely spaced on the mount. Adjacent magnets of the movable portion magnet means as well as adjacent magnets of the stationary magnet means have the same magnetic poles. Furthermore, the opposite poles of two magnets, which are distant in a vertical direction, have the same polarity. It is an object of the present invention to provide a dynamic vibration absorber in which a single movable weight portion is supported in such a manner that it can cope with vibration in any direction of two horizontal dimensions in order to control the vibrations of a target structure while enabling easy installation. A solution of this object is achieved by the dynamic vibration absorber according to the appended claim 1. The appended subclaims are directed towards advantageous embodiments of the inventive dynamic vibration absorber. According to the structures and characteristics of the present invention described above, in one aspect, when the movable weight portion shifts from its stationary state, i.e., when the center of the movable portion magnetic train deviates from the center of the fixed magnetic train which opposes the movable portion magnet train, an attracting force acts between the different magnets which oppose each other when the movable weight portion is in a stationary state and returns the magnets to their original states. When the position of the magnet in the magnet train deviates, the magnet approaches the adjacent magnet having a magnetic pole different from that magnet, so that a repelling force is generated therebetween. These forces act as a restoring force which returns the the movable portion magnet train and the fixed portion magnet trains, which have been offset in the radial direction, to their original positions. Further, since the magnets are disposed coaxially, the same restoring force can be obtained relative to the displacement in any direction of horizontal two-dimensions. The vibration energy transmitted to the target structure by a vibratory disturbance, such as an earthquake, is effectively absorbed by the vibrations of the movable weight portion, and the resonance of the target structure can thus be eliminated. Further, vibrations in any direction of horizontal two-dimensions can be attenuated. At the same time, the conductor plate of the magnetic damper mean motions relative to the magnetic field in the yoke in which the magnets are disposed on the opposed end surfaces thereof. Therefore, an eddy current is generated in the conductor plate, and the motion of the conductor plate is restricted and damped due to the interaction between the eddy current and the magnetic field in the yoke. Consequently, vibration energy is absorbed and damping is thus performed. The natures and further features of the present invention will be made more clear from the following preferred embodiments made with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a vertical sectional view showing a first embodiment of a dynamic vibration absorber according to the present invention; Fig. 2 is a horizontal sectional view of the dynamic vibration absorber of Fig. 1; and Fig. 3 is an enlarged view of a yoke portion shown in Fig. 1 in a modified example. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described hereunder with reference to the accompanying drawings. Fig. 1 is a vertical sectional view showing a first embodiment of a dynamic vibration absorber according to the present invention. Fig. 2 is a horizontal sectional view of Fig. 1. Referring to Figs. 1 and 2, a movable weight portion 1, serving as a vibration absorber, is provided with a movable portion magnet train 2 consisting of cylindrical magnets. The cylindrical magnets are disposed coaxially in the form of multiple cylinders in such a manner that the adjacent magnets have different magnetic poles. The movable weight portion 1 and the movable portion magnet train 2 are disposed in a cylindrical vessel 3 having upper and bottom plates 4 and 5, on a stationary side, opposing the movable portion magnet train 2, constituting a fixed portion. In the space formed by the upper and bottom plates 4 and 5 of the cylindrical vessel 3 are accommodated respective elements of the dynamic vibration reducer, a fixed portion magnet train 6 mounted on the inner surface of the upper plate 4 and a fixed portion magnet train 6 mounted on the inner surface of the bottom plate 5. Each of the fixed portion magnet trains 6 has the same shape as corresponding one of the movable portion magnet train 2 and is separated from the movable portion magnet train 2 in the vertical direction through a predetermined gap 7. In each of the fixed portion magnet trains 6, magnetic poles are disposed such that they respectively oppose the cylindrical magnets having magnetic poles different from the magnetic poles in the movable weight portion 1 in a stationary state. Four bearings (spherical bearings) are fixed equiangularly on each of the upper and bottom surfaces of the movable weight portion 1 on a horizontal plane and receptacles 9 are fixed on each of the upper and bottom plates 4 and 5 which oppose the bearings 8. The contact of each of the bearings 8 with the corresponding receptacle 9 makes the vertical position of the movable weight portion 1 restricted. to thereby maintain the gap 7 to a fixed value. In this embodiment, it is thus possible to adjust the rigidity, with which the movable weight portion 1 is supported in the horizontal direction, by adjusting the magnetomotive forces generated by the magnets in the movable portion magnet train 2 and fixed portion magnet trains 6 and also adjusting the gap 7. Further, in order to optimize the damping force which acts on the movable weight portion 1, a magnetic damper means is constituted in this embodiment by providing four conductor plates 10 and four yoke means 11. Each of the yoke means 11 is composed of a base portion to be secured to the side wall surface of the vessel 3 and york portions extending from the base portion parallelly so as to provide substantially ⊐ - shape. The conductor plates 10 are mounted on the peripheral surface of the movable weight portion 1 equiangularly on a horizontal plane in such a manner that each of the conductor plates 10 is sandwiched between two magnets 12 disposed at distal ends of the yoke portions of a yoke means 11 fixed to the side peripheral surface of the cylindrical vessel 3 with gap 13 therebetween. It is therefore possible to adjust the damping force which acts on the movable weight portion 1 by adjusting the magnetomotive forces generated by the magnets 12, the gap 13 and the number of magnetic dampers provided. The excellent performance of the dynamic vibration reducers, i.e., a restoring force which returns the movable weight portion 1 to a stationary position, can be obtained by adjusting the distances between the multiple cylinders according to the displacement required for the movable weight portion 1. That is, the distances of the cylindrical magnets can be adjusted such that, for example, the central N pole of the movable portion magnet train 2 is not attracted by the S pole located beyond the N pole in the fixed portion magnet train 6 located adjacent to the central N pole. The function of this embodiment will now be described. When the movable weight portion 1 shifts from its stationary state, i.e., when the center of the movable portion magnetic train 2 deviates from the center of the fixed magnetic train 6 which opposes the movable portion magnet train 2, an attracting force acts between the different magnets which oppose each other when the movable weight portion 1 is in a stationary state and returns the magnets to their original states. Furthermore, when the position of the magnet in the magnet train deviates, the magnet approaches the adjacent magnet having a magnetic pole different from that magnet, so that a repelling force is generated therebetween. These forces act as a restoring force which returns the movable portion magnet train 2 and the fixed portion magnet trains 6 which have been offset in the radial direction to their original positions. Further, since the magnets are disposed coaxially, the same restoring force can be obtained relative to the displacement in any direction of horizontal two-dimensions. In a modification of the first embodiment, the fixed portion magnet train 6 is composed of permanent magnets and electromagnets. In this way, the magnetomotive force generated by the fixed portion magnet train 6 can be made variable, and the support rigidity of the movable weight portion 1 in the horizontal direction can thus be readily adjusted. In this embodiment, since the movable weight portion 1 is horizontally supported in a completely non-contact state except for a portion thereof in which the vertical position is restricted by the bearings 8 and the receptacles 9, a contact friction caused by vibrations or a fatigue of the support member can be eliminated. As a result, a highly reliable vibration absorber can be provided. Fig. 3 is an enlarged view of the yoke means 11 shown in Fig. 1. In Fig. 3, the yoke 11 (yoke portions 11a, 11b) with the magnets 12 (12a, 12b) provided on the opposing upper and lower surfaces of the distal end thereof is coupled to a fixed block 54 through a guide bar 53. The vertical movement of the guide bar 53 relative to the fixed block 54 is restricted by locking washers 55. An upper portion of the guide bar 53 is right-handedly threaded to form a right-handed screw 56, and a lower portion thereof is left-handedly threaded to form a left-handed screw 57. The right-handed screw 56 is in thread engagement with an upper yoke portion 11a, and the left-handed screw 57 is in threaded engagement with a lower yoke portion 11b. The guide bar 53 is not in threaded engagement with the fixed block 54. Consequently, the rotation of one end of the guide bar 53 enables the upper and lower yoke portions 11a and 11b to be rotated in opposite directions at the same time through the same distance, i.e., it allows the gaps 13a and 13b between the conductor plate 10 and the upper and lower magnets 12a and 12b to be adjusted at the same time by the same amount. The yoke portions 11a and 11b are in contact with the fixed block 54 through a sliding surface 58 to ensure a magnetic path cross-sectional area as a magnetic circuit. As will be understood from the foregoing description, the dynamic vibration absorber of the present invention includes a movable weight portion serving as a dynamic vibration absorber, a movable portion magnet train provided in the movable weight portion in which cylindrical magnets are disposed coaxially in such a manner that adjacent cylindrical magnets have different magnetic poles, fixed portions provided in opposed relation to the movable portion magnet train, and a fixed portion magnet train provided on each of the fixed portions in which magnetic poles are disposed such that they respectively oppose the cylindrical magnets in the movable weight portion having magnetic poles different from the magnetic poles in a stationary state. Since the movable weight portion is horizontally supported by a magnetic force which acts between the movable weight portion and the fixed portion, it is supported in any direction of horizontal two-dimensions with the same rigidity. Consequently, the damping effect can be obtained regardless of the direction of vibrations using the single movable weight. Further, when the damping element is composed of the conductor plate and the yoke, the motion of the movable weight portion is restricted and damped in a non-contact state thereof to absorb vibration energy. Thus, a highly reliable damping effect can be obtained.

Claims: A dynamic vibration absorber comprising: a movable weight portion (1) serving as a dynamic vibration absorber; and a fixed portion (3) provided in opposed relationship to the movable weight portion, characterized by a movable portion magnet means provided for the movable weight portion (1), said movable portion magnet means comprising a magnet train (2) including a plurality of cylindrical magnets disposed coaxially in such a manner that adjacent cylindrical magnets have different magnetic poles; a fixed portion magnet train (6) provided on the fixed portion and comprising a plurality of magnets having magnetic poles different, in a stationary state, from magnetic poles of the cylindrical magnets disposed to oppose respectively the corresponding magnets on the fixed portion with a predetermined gap (7) therebetween, wherein said movable weight portion is horizontally supported by a magnetic force which acts between the movable weight portion and the fixed portion. A dynamic vibration absorber according to claim 1, characterized in that the predetermined gap (7) is adjustable. A dynamic vibration absorber according to claim 1, characterized in that said movable weight portion (1) has a cylindrical outer appearance and is disposed in a cylindrical vessel (3) having top and bottom portions and a peripheral side portion disposed between the top and bottom portions and said fixed portion magnet train (6) is disposed on each of the top and bottom portions of the cylindrical vessel. A dynamic vibration absorber according to claim 3, characterized in that a plurality of bearings (8) are disposed on top and bottom surfaces of the movable weight portion (1) and a plurality of bearing receptacles (9) are disposed on inner surfaces of the top and bottom portions of the cylindrical vessel (3) so as to receive corresponding bearings to thereby maintain the gap (7) between the movable portion magnet train (1) and the fixed portion magnet train (6). A dynamic vibration absorber according to claim 4, characterized in that bearings (8) and bearing receptacles (9) are disposed and separated with equal angles, respectively, in a horizontal plane. A dynamic vibration absorber according to claim 3, characterized in that it further comprises a magnetic damper means (10, 12) having a plurality of conductor plates (10) mounted on an outer peripheral surface of the movable weight portion (1) and a plurality of yoke means (11) secured to an inner surface of the peripheral side portions of the cylindrical vessel (3) at portions corresponding to the conductor plates, each of said yoke means having a pair of yoke portions facing each other, and a pair of magnets (12) are provided on the facing surfaces of the paired yoke portions with gap (13) into which the corresponding conductor plates are inserted with gap. A dynamic vibration absorber according to claim 6, characterized in that the conductor plates (10) and the yoke means (11) are provided with equally spaced angles, respectively, in a horizontal plane. A dynamic vibration absorber according to claim 7, characterized in that the numbers of the condutor plates (10) and the yoke means (11) are adjustable. A dynamic vibration absorber according to claim 6, characterized in that each of said yoke means (11) comprises a pair of a yoke portions (11a, 11b) and a yoke portion fixing member (7), said yoke portion fixing member having an inner surface to which one ends of the paired yoke portions contact slidably and said yoke portions having other one ends facing each other. A dynamic vibration absorber according to claim 9, characterized in that the one ends of the yoke portions (11a, 11b) are secured to the yoke portion fixing member (54) by means of screw (53) to be adjustable.

Inventors: AIDA YASUHIKO, HATTORI KIYOSHI, MANOME EIJI, MIYANO HIROSHI, NASUDA TOSHIAKI, SAKURAI YOSHIYUKI, AIDA, YASUHIKO, HATTORI, KIYOSHI, MANOME, EIJI, MIYANO, HIROSHI, NASUDA, TOSHIAKI, SAKURAI, YOSHIYUKI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1994
Main classification: F16F7
IPC codes: F16F15, F16F7